Isoflurane preconditioning improves learning and memory functions in focal cerebral ischemia-reperfusion injury in rats by upregulating hippocampal AMPA receptor GluR1 subunit

Objective To investigate the effect of isoflurane preconditioning on rat learning and memory in cerebral ischemia-reperfusion injury and its possible mechanism. Methods Thirty-six adult male Sprague-Dawley rats were randomly divided into a sham operation group, a cerebral ischemia-reperfusion group, and an isoflurane preconditioning group (n=12 in each group). A model of middle cerebral artery occlusion and ischemic-reperfusion was induced by a modified intraluminal suture method. The rats of the isoflurane preconditioning group inhaled 1.5% isoflurane for 1 hour per day for 5 d. At 24 h after the last preconditioning, a model of MCAO was made. At 24 h after MCAO, the infarct volume was detected by using 2, 3, 5 chlorinated diphenyl tetrazolium staining. At day 1, 3, 7, and 14 after MCAO, the modified Neurological Severity Score (mNSS) were performed. At day 9 after MCAO, the Morris water maze test was used to evaluate the learning and memory of rats. At day 14, Western blotting was used to detect the protein expression level of hippocampal tissue glutamate receptor 1 (GluR1) on the side of ischemia. Results No obvious infarcts were observed in the rats of the sham operation group. The infarct volume in the isoflurane preconditioning group was significantly smaller than that of the cerebral ischemia-reperfusion group (26.383%±3.128% vs. 19.107%±1.661%; P<0.05). No neurological deficit was observed in the sham operation group (score 0). The mNSS scores at day 1, 3, 7, and 14 after MCAO in the isoflurane preconditioning group were decreased significantly (day 1: 9.000±1.195 vs. 11.500±1.414; day 3: 6.6250±1.407 vs. 6.625±1.407vs. 6.625±1.407; day 7: 5.875±0.707 vs. 7.375±1.407; and day 14: 3.375±1.187 vs. 5.125±1.246; all P<0.05). The Morris water maze showed that the escape latencies at day 1-5 after MCAO in the isoflurane preconditioning group were all significantly shorter than those in the cerebral ischemia-reperfusion group (day 1: 95.992±15.734 s vs. 103.008±11.654 s; day 2: 70.949±14.708 s vs. 94.705±14.709 s; day 3: 39.660±7.413 s vs. 65.716±10.155 s; day 4: 22.692±5.778 s vs. 35.240±8.553 s; day 5: 14.906±4.336 s vs. 22.890±10.381 s; all P<0.05). The numbers of crossing platform (4.556±1.333 vs. 2.889±1.536 ) and the percentages of time spent in the target quadrant (33.014%±5.223% vs. 21.978%±6.697%) in the isoflurane preconditioning group were significantly increased than in the cerebral ischemia-reperfusion group (all P<0.01). The levels of hippocampal GluR1 protein on the ischemic sides in the sham operation group, ischemia-reperfusion group, and isoflurane preconditioning group were 0.871±0.153, 0.456±0.130, and 0.689±0.126, respectively. There were significant differences among the 3 groups (F=18.329, P<0.001) and the isoflurane preconditioning group was significantly higher than the ischemia-reperfusion group (P<0.05). Conclusions Isoflurane preconditioning can improve the learning and memory in cerebral ischemia-reperfusion in rats, its mechanism may be associated with the uprelagating GluR1 expression in the hippocampus. Key words: Isoflurane; Brain Ischemia; Maze Learning; Memory; Receptors, AMPA; Receptors, Ionotropic Glutamate; Neuroprotective Agents; Disease Models, Animal; Rats